In certain types of circular knitting machines, notably the Textile Machine Works knitting machine, types of Mark III, Mark IIIS, and Mark IV, a microswitch is mounted on the machine adjacent the pattern chain and cam drum, and is operated through a lever mechanism, selectively activated by protruding lugs on the pattern chain and cams on the drum. The lever mechanism, when thusly activated, engages the contact arm of the microswitch to complete a circuit, sending impulses to a solenoid to selectively shift the drive belt of the needle cylinder between a fast and slow speed pulley.
Considerable difficulty has been encountered with the microswitch in that either oil works its way into the interior of the microswitch and causes a carbon buildup on the contacts, preventing good electrical contact between the activator arm and one of the contacts, or else the activator arm, which is a thin metallic plate, breaks after a short time due to the constant wear.
As a result such microswitches must be replaced on the knitting machines periodically, sometimes as often as monthly, causing added expense and down time of the machine. Further, if the contact strip breaks during usage, the drive belt is not shifted from the fast to the slow speed pulley prior to the pattern shift and considerable damage can be done to the needle cylinder, resulting in the machine being down for several hours.
Efforts to solve this problem have, so far, been unsuccessful.